Functional acclimation to solar UV-B radiation in Gunnera magellanica, a native plant species of southernmost Patagonia

The ecosystems of Tierra del Fuego (in southern Patagonia, Argentina) are seasonally exposed to elevated levels of ultraviolet‐B radiation (UV‐B: 280–315 nm), due to the passage of the ‘ozone hole’ over this region. In the experiments reported in this article the effects of solar UV‐B and UV‐A (315–400 nm) on two UV‐B defence‐related processes: the accumulation of protective UV‐absorbing compounds and DNA repair, were tested. It was found that the accumulation of UV‐absorbing sunscreens in Gunnera magellanica leaves was not affected by plant exposure to ambient UV radiation. Photorepair was the predominant mechanism of cyclobutane‐pyrimidine dimer (CPD) removal in G. magellanica. Plants exposed to solar UV had higher CPD repair capacity under optimal conditions of temperature (25 °C) than plants grown under attenuated UV. There was no measurable repair at 8 °C. The rates of CPD repair in G. magellanica plants were modest in comparison with other species and, under equivalent conditions, were about 50% lower than the repair rates of Arabidopsis thaliana (Ler ecotype). Collectively our results suggest that the susceptibility of G. magellanica plants to current ambient levels of solar UV‐B in southern Patagonia may be related to a low DNA repair capacity.     

Translation of RNA from Eggs During Post-Diapause Development of Bombyx mori

Eggs of Bombyx mori are aroused from diapause by long-term chilling and develop when transferred to 25°C. During the first 20 hr of post-diapause development, the polysome content and the presumed rate of protein synthesis increase about 3-fold, while the ribosome content and the total RNA content increase only 1.1-fold. In this study, total RNAs were extracted from chilled eggs (termed 0 hr of development), and post-diapause eggs at 10 and 20 hr of development. The RNAs were purified further by high pressure liquid chromatography to remove RNA-like oligonucleotides. On translation in a protein-synthesizing system derived from wheat germ with a subsaturating amount of RNA, no difference was found in the relative amounts of translatable mRNA activity at 10 and 20 hr of development from that at 0 hr. Moreover, the translation products of the different RNA preparations in a rabbit reticulocyte lysate system appeared very similar when separated by gel electrophoresis and located by fluorography. These facts suggest that protein synthesis in early post-diapause development is controlled at a translational level.     

Studies on the metabolism of a sulfur-oxidizing bacterium V. Comparative studies on sulfur and sulfite oxidizing systems of Thiobacillus thiooxidans

Properties of the oxidation systems of sulfur and sulfite ofa sulfur oxidizing bacterium, Thiobacillus thiooxidans, arecompared by using various inhibitors. Oxidation of sulfur isinhibited by a low concentration of monoiodoacetic acid, NEMand pCMB. Inhibition by pCMB is diminished by the addition ofan equivalent amount of cysteine to that of added pCMB. Althoughinhibition by pCMB is also observed in the oxidation of sulfite,it is not diminished by the addition of excess cysteine andthe extent of inhibition is lower than that in the oxidationof sulfur. Metal chelating agents, such as DDC, 8-hydroxyquinoline, salicylaldoximeand neocuproine have inhibitory effects on the oxidation ofsulfur but do not affect the oxidation of sulfite. Carbon monoxide inhibits the oxidation of sulfur photo-irreversiblyand the oxidation of sulfite photo-reversibly. Alcohols and organic acids, inhibit the oxidation of both sulfurand sulfite. The cell-free extract prepared by sonic disruptionof cells can oxidize sulfite, but not sulfur. The sulfur oxidizingextract can be, however, prepared by disruption under a nitrogenatmosphere. Both the soluble and participate fractions are requiredfor the oxidation of sulfur, while sulfite oxidation is catalyzedby the participate fraction alone. ¹Partly supported by a grant from the Ministry of Education.     

Temporal photosynthetic carbon isotope signatures revealed in a tree ring through 13CO2 pulse-labelling

Using a combined method of pulse-labelling trees and analysing detailed distribution of ¹³C tracer within tree rings, we studied how photo-assimilates incorporated on a given day are then distributed in a tree ring. A branch of a 4-year-old Cryptomeria japonica D.Don tree growing in Tsukuba, Japan was pulse-labelled with non-radioactive ¹³CO₂ on two occasions: 29 May 2001 and 18 September 2001. Two discs were cut from the stem on 4 March 2002, one immediately under and the other 0.5 m below the branch and put through high-resolution δ ¹³C analysis. δ ¹³C peaks were observed in both the earlywood and latewood of the concerned tree ring, corresponding to each pulse-labelling date. The earlywood peaks was broader than the latewood peaks, possibly reflecting seasonal variation of the width of wood developing zone. Half-widths of the peaks were measured and used as indicators for the potential time resolution of tree-ring isotope analysis. The half-widths of the peaks indicated a time resolution no finer than 8.7–28 and 33–42 d in the early and latewood, respectively. Holocellulose extraction yielded only a slight change to the shape of the δ ¹³C peaks. ¹³C tracer pulse-labelled in May and September reached tangentially different locations in the lower disc, suggesting a seasonal change in the pathway of carbohydrates. Local consumption of spring assimilates and long-distance downward transport of autumn assimilates were also suggested.     

Timing of emergence of males and females of Ephoron shigae (Ephemeroptera: Polymitarcyidae)

SUMMARY. 1. The winged adults of Ephoron shigae swarming over the water surface were collected by successive random sweeps during their daily emergence period, and the changes in sex and stage composition were examined, in the lower reach of the Asahi River in western Japan.
2. The emergence occurred mainly during a 1¹/₂ h period beginning some time after sunset. Male sub-imagos emerged synchronously and moulted to imagos in a 25 min period immediately prior to an abrupt increase of female emergence.
3. This timing of male emergence may be considered the result of selection of males to decrease the risk of death before mating, and for all the males to have an equal opportunity to mate.     

The role of a glyoxylate-glycolate system in chloroplasts of higher plants

Photoreduction of glyoxylate and oxidation of glycolate wereinvestigated using unwashed chloroplasts from spinach leaves.A glyoxylateglycolate system operated in light and under aerobicconditions. Accompanying the photoreduction of glyoxylate andthe oxidation of glycolate, was the disappearance of inorganicphosphate. Photoreduction of oxalate was also observed in illuminatedchloroplasts. The reaction rate was, however, much lower thanthat for the photoreduction of glyoxylate. (Received August 4, 1969; )     

Ontogenetic change of distributional patterns of pore systems in Cythere species and its phylogenetic significance

Species of Cythere (Ostracoda, Crustacea) have about one hundred normal pore systems on each valve of the carapace. These can be classified into five types on the basis of morphological features. They were examined in the light of intraspecific variation and interspecific difference. Each of the five pore systems has its own mode of ontogenetic increase in number. Comparison among fourteen Cythere species shows that the distributional patterns are completely identical in the A-3 stage, but that they are classified into four and eight groups in the A-2 and A-1 stages, respectively. In the adult stage the pattern becomes diversified among the fourteen species, though homologous relationships are still recognized between different species. The similarity and difference of the pore patterns, which are traceable until the last ontogenetic stage, can be used to determine phylogenetic relationships. These findings were applied to the reconstruction of phylogeny of the eleven living and three extinct species of Cythere. □ Crustacea. Ostracoda , Cythere, Ontogeny. Phylogeny, pore system, pore canal. speciation, laroal morphology.     

Fractal Analysis of Plant Root Systems

The morphology of root systems of crop plants was analysed byfractal geometry using an image processing system. Results indicatethat these root systems have a fractal structure (D; 1.48     

Stimulation of Spermatid Phosphofructokinase by Fructose 2,6-Bisphosphate from Rat Testes

Effect of fructose 2, 6-bisphosphate on 6-phosphofructokinase (ATP: D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) in spermatid extract from rat testes was studied. Fructose 2, 6-bisphosphate stimulated the enzyme greatly by increasing its affinity for fructose 6-phosphate and relieving the inhibition by ATP. Fructose 2, 6-bisphosphate (0.8 μM) was required for 50% activation of 6-phosphofructokinase (PFK). In addition, fructose 2, 6-bisphosphate, AMP and fructose 6-phosphate acted cooperatively to stimulate the activity of PFK. This stimulation may play an important role in the regulation of glycolysis in spermatids of rat testes.